1. Field of the Invention
The invention is drawn to a method for the production of ethers from polyols, catalysts for use in producing the ethers, and the use of the ethers as renewable fuels.
2. Description of the Prior Art
Existing techniques for the preparation of ethers are variants of the classic Williamson ether synthesis, and generally require dangerously volatile and highly carcinogenic alkylating agents such as methyl iodide or dimethyl sulfate. Moreover, the reactions also typically require a non-aqueous and expensive co-solvent, such as DMSO or dimethylformamide.
Many simple ethers (such as diethylether) are known compounds, and are volatile, flammable solvents. Diethylether, for example, is used in cellulose acetate production and as a starter fluid for small gasoline engines. Other synthetic ethers include cyclic furans: tetrahydrofuran (THF) and 1,4-dioxane are produced commercially as solvents. In 1990, US production of dioxane was between 10.5 and 18.3 million pounds. About 200,000 tons of THF are produced annually, mainly as an industrial solvent for PVC and in varnishes.
In addition to the market for known ethers, there is a clear future need for renewable materials and chemicals to replace those from dwindling petroleum feedstocks, and biobased products from biorefinery carbohydrates are a high priority. The energy potential to supplement gasoline and diesel usage in the U.S. alone is huge, currently approximately 15 and 6×1010 gal/year, respectively. In addition to fuels, which despite their high volume are relatively low value products, other materials are required to replace lubricant oils and greases, emulsifiable oils, and various substitute solvents, including kerosene. As of 2010, glycerol, sorbitol, and xylitol/arabinitol are all in the DOE “top 10” chemical opportunities from carbohydrates (Bozell and Petersen. 2010. Technology development for the production of biobased products from biorefinery carbohydrates—the US Department of Energy's “Top 10” revisited. Green Chem. 12:539-554). In fact, crude glycerol from biodiesel production accounts for ˜1 million tons/year, with projected prices as low as $0.11/kg. Thus, the need remains for improved technologies for the production of ethers, and for the production of renewable fuels and other products from existing agriculture-based substrates.